The present invention relates to paving machines, and more particularly to strike-off devices for paving screeds.
Screed assemblies 1 used with paving machines to level paving material, typically asphalt, applied by the machine onto a generally horizontal base surface 2 are well known, an example of such being depicted in FIGS. 1 and 2. Such screed assemblies 1 often include both a main screed 3 and one or more pairs of screed extensions 4 connected with the main screed 3. The screed extension 4 may either be fixedly attached (e.g., bolted) to an end of the main screed 3 (or an outer end of another screed extension 4) or movably attached to the main screed 3. Movably attached screed extensions 4 are commonly referred to as "extendible screeds" and are laterally displaceable with respect to the main screed 3, typically by means of hydraulic cylinders (not shown) so as to either be extended outwardly substantially beyond the outer ends 3b of the main screed 3 or retracted into centralized positions. Both types of screed extensions 4 enable the screed assembly 1 to be adjusted for use in paving different base surfaces 2 of various widths.
Further, screed assemblies 1 having one or more strike-off devices 5 disposed frontwardly (i.e., with respect to the direction of paving machine travel 11) of the screed sections 3, 4 are also known. Particularly with paving screeds 1 having front-mounted extendible screeds 4, the strike-off devices 5 prevent paving material from accumulating in front of the main screed 3 and thus prevent uneven distribution of paving material across the width of the screed assembly 1. Such known strike-off assemblies 5 typically include a strike-off member or plate 6 movably attached to the main screed 3 such that the vertical position of the plate 6 is adjustable. The strike-off member/plate 6 has a working edge 6a at the lower end of the plate 6 which establishes a first height/thickness of paving material prior to leveling by the working surfaces 3a, 4a of the screed assembly 1. Thus, it is important to control the vertical position of the strike-off working edge 6a to ensure that it is at a desired distanced above the working surfaces 3a, 4a (see FIG. 2) determined to provide optimal performance of the paving screed assembly 1.
Further, in order to control the depth of the finished "mat" of paving material, the "angle of attack" .alpha. of the screed assembly 1 (FIG. 2) may often have to be adjusted. First, the main screed 3 is "tilted" frontwardly or rearwardly to position the main screed working surface 3a at the desired angle .alpha.. As the strike-off plate 6 and screed extensions 4 are attached to the main screed 3, varying the angle a of the main screed 3 causes both the screed extensions 4 and the strike-off plate 6 to move vertically upwardly or downwardly. Thus, the screed extension 4 must first be adjusted vertically to the proper height, which in the known assembly 1 of FIGS. 1 and 2, requires moving two cylindrical posts 8 at the upper end of each screed extension 4 within an associated bushing 9 extending through a support member 7, a pair of the support members 7 connecting each screed extension 4 to the main screed 3. Therefore, four separate adjustments may be required to properly position the two extensions 4, although preferably a vertical positioning device 15 is configured to simultaneously adjust the pair of posts 8 for each screed extension 4 so that the operator need only make two adjustments (i.e., one for each extension 4).
Further, the strike-off plate 6 must also be adjusted to position the strike-off working edge 6a at the proper height, which with the two devices 5 depicted in FIGS. 1 and 2, requires adjusting two pairs of threaded rods 5a which connect each plate 6 to the main screed 3 (specifically to a separate support member 7). Therefore, properly positioning the strike-off device 5 requires another four separate adjustment steps. Thus, whenever the angle of attack a of the main screed 3 is adjusted, at least six and potentially eight separate adjustment steps may be required to position both the screed extensions 4 and the strike-off plate 6 of the known strike-off device 5 at proper working heights.
Therefore, it is desirable to provide a strike-off device for a screed assembly in which the number of adjustment steps required to properly position both the screed extensions and the strike-off plates after a change in the angle of attack a is less than that required for previously known strike-off devices.